In almost every case, the mould problem was not caused by the building, but the lifestyle of the occupants. The windows would all be shut tight “to keep the cold out”, and/or there would be laundry drying in front of the heater. Some would never use the exhaust fan in the bathroom… the list goes on.
That would go some way to explaining why people move from apartment to apartment and can never seem to find one that doesn’t have a mould problem. I’m not saying that’s the case in every instance, but it’s worth considering. There is another issue, though, there has to be a better way of ventillationg flats than opening windows in winter.